The present invention relates to organic electronic devices, in particular organic electroluminescent devices, which comprise aromatic nitrogen heterocyclic compounds.
The structure of organic electroluminescent devices (OLEDs) in which organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. However, further improvements are still desirable before these devices can be used for high-quality and long-lived displays. Thus, there is currently still a need for improvement, in particular, in the lifetime, the efficiency and the operating voltage of organic electroluminescent devices. Furthermore, it is necessary for the compounds to have high thermal stability and to be sublimable without decomposition.
Improvements are still desirable, in particular, in the charge-injection and -transport materials since it is precisely the properties of the charge-transport materials that also have a significant influence on the above-mentioned properties of the organic electroluminescent device. In particular, there is a need for improvement in electron-transport materials and hole-injection or hole-transport materials which simultaneously result in good efficiency, a long lifetime and a low operating voltage. The properties of these materials, in particular, are frequently also limiting for the lifetime, the efficiency and the operating voltage of the organic electroluminescent device.
AlQ3 has already been used for some time as electron-transport material (for example U.S. Pat. No. 4,539,507), but has a number of disadvantages: it cannot be vapour-deposited without a residue since it partially decomposes at the sublimation temperature, which represents a major problem, in particular, for production plants. This has the consequence that the vapour-deposition sources must repeatedly be cleaned or changed. Furthermore, decomposition products of AlQ3 reach the OLED, where they contribute to a shortened lifetime and reduced quantum and power efficiency. In addition, AlQ3 has low electron mobility, which results in higher voltages and thus in lower power efficiency. In order to avoid short circuits in the display, it would be desirable to increase the layer thickness; this is not possible with AlQ3 owing to the low charge-carrier mobility and the resultant increase in voltage. The charge-carrier mobility of other electron conductors (U.S. Pat. No. 4,539,507) is likewise too low to build up thicker layers therewith, with the lifetime of the OLED being even worse than on use of AlQ3. The inherent colour (yellow in the solid state) of AlQ3 also proves to be unfavourable, possibly resulting in colour shifts due to reabsorption and weak re-emission, especially in the case of blue OLEDs. Blue OLEDs can only be produced here with considerable adverse effects on efficiency and colour location.
Apart from various triarylamine derivatives or carbazole derivatives, the hole-injection or hole-transport materials used in organic electroluminescent devices in accordance with the prior art are, in particular, also hexaazatriphenylene derivatives, in particular those which are substituted by cyano groups (for example WO 01/049806). There likewise still continues to be a need for improvement here in respect of the lifetime, the efficiency and the operating voltage.
Thus, there continues to be a demand for electron-transport materials and hole-injection and hole-transport materials which result in good efficiencies and at the same time in long lifetimes in organic electroluminescent devices. Surprisingly, it has now been found that organic electroluminescent devices which comprise certain nitrogen heteroaromatic compounds—indicated below—as electron-transport materials or as hole-injection or hole-transport materials have significant improvements over the prior art. Using these materials, it is possible simultaneously to obtain high efficiencies and long lifetimes.
Heptaazaphenalene derivatives, in particular those which are substituted by aromatic groups, alkoxy groups or amino groups, are already known in the literature as protection against UV radiation (for example WO 07/006807) or flameproofing agents (for example WO 01/021698). Use of such compounds in organic electronic devices is not known.